Preparation method of vinyl acetate

Abstract

The invention discloses a preparation method of vinyl acetate, and belongs to the field of organic synthesis. According to the method, a derivative of lactic acid is taken as a substrate, in the presence of a photosensitizer, a cobalt catalyst and alkali, a decarboxylation dehydrogenation reaction can be realized through blue light irradiation, and vinyl acetate is prepared. The method has the advantages of high selectivity, high yield and mild reaction conditions, and is suitable for popularization and application of industrial production.

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis, and particularly relates to a method for preparing vinyl acetate. Background Art

[0002] Vinyl acetate is an important chemical product with a wide range of uses. It is mainly used to manufacture synthetic fiber nylon, and can also be copolymerized with other polymer monomers to form copolymer resins. For example, vinyl acetate can form polyvinyl acetate through self-polymerization. Polyvinyl acetate is often used to make toy plush, non-woven gum base, adhesives, etc.; polyvinyl acetate can be hydrolyzed to prepare polyvinyl alcohol, which is widely used in the production of coatings, adhesives, emulsifier film products, etc. In addition, vinyl acetate can be copolymerized with ethylene and then hydrolyzed to obtain ethylene-vinyl alcohol copolymer, which is a high gas barrier material with gas barrier properties dozens of times higher than the commonly used barrier material polyvinylidene chloride.

[0003] At present, the main methods for synthesizing vinyl acetate in industry are acetylene method and ethylene method. The ethylene method is divided into Bayer and USI methods, and the ethylene method accounts for more than 80% of the total production capacity. The acetylene method uses acetylene and acetic acid as raw materials, zinc acetate-activated carbon as catalyst, and reacts at 180~200℃ to prepare vinyl acetate. This method has many by-products, such as acetaldehyde, crotonaldehyde, ethylene glycol diacetate, etc., and the single-pass conversion rate is low and the reaction temperature is high. The ethylene method uses ethylene, acetic acid and oxygen as raw materials to prepare vinyl acetate. The Bayer method uses Pd-Au / SiO2 as the main catalyst and potassium acetate as the co-catalyst. The reaction temperature is 140~180℃ and the pressure is 0.6~1.1MPa; the USI method uses Pd-Pt / Al2O3 as the catalyst, the reaction temperature is 125~145℃, and the pressure is 0.15~0.25MPa. Both methods also have the problem of more by-products, such as acetaldehyde, ethyl acetate and polymers, and the single-pass conversion rate is also low. Moreover, both ethylene and acetylene rely on fossil resources, which is not in line with the goals of green development and carbon neutrality. Summary of the invention

[0004] The present invention aims at the deficiencies of the prior art and provides a method for preparing vinyl acetate. The method uses a derivative of lactic acid as a substrate, is greener, has high selectivity, high yield and mild reaction conditions.

[0005] The method for preparing vinyl acetate of the present invention comprises the following steps:

[0006] 2-Acetoxypropionic acid, a photosensitizer, a cobalt catalyst, a base and a solvent are added into a reaction container, and vinyl acetate is prepared by a decarboxylation and dehydrogenation reaction under an inert gas atmosphere and blue light irradiation.

[0007] The photosensitizer structural formula is as follows:

[0008]

[0009] Wherein, R1-R8 represents hydrogen or C1-C6 alkyl, alkoxy or halogenated alkane, such as methyl, trifluoromethyl or tert-butyl; X represents halogen, such as fluorine; Ar represents an aromatic group; Y - Represents anions, such as ClO4 - or PF6 - wait.

[0010] Furthermore, the photosensitizer preferably has the following structure:

[0011]

[0012] The photosensitizer is commercially available.

[0013] The general structural formula of the cobalt catalyst is shown below:

[0014]

[0015] Wherein, L represents a ligand, such as pyridine, 4-methoxypyridine, etc.; X represents a halogen, such as chlorine, bromine, etc.

[0016] Furthermore, the cobalt catalyst preferably has the following structure:

[0017]

[0018] The base includes but is not limited to one or more of Cs2CO3, Na2CO3, NaHCO3, K2CO3, KHCO3, K3PO4, K2HPO4, Na3PO4, Na2HPO4, Me4NOH, Me4NHCO3, and (Me4N)2CO3.

[0019] The solvent includes, but is not limited to, one or more of halogenated alkanes, ethers, and amide solvents.

[0020] Further, the solvent is selected from one or more mixed solvents of ethylene glycol dimethyl ether, tetrahydrofuran, acetonitrile, diethylene glycol dimethyl ether, dimethyl sulfoxide, N,N-dimethylformamide, N,N-diethylacetamide, and ethylene dichloride. Preferably, the mixed solvent is composed of ethylene glycol dimethyl ether and water, and the volume ratio of the two is 18:1.

[0021] Furthermore, the molar ratio of 2-acetoxypropionic acid to the photosensitizer is 200:1 to 5:1, preferably 100:1 to 50:1.

[0022] Furthermore, the molar ratio of 2-acetoxypropionic acid to the cobalt catalyst is 50:1 to 5:1, preferably 20:1 to 10:1.

[0023] Furthermore, the molar ratio of 2-acetoxypropionic acid to the base is 10:1 to 1:1, preferably 1:1.

[0024] Furthermore, the concentration of 2-acetoxypropionic acid in the reaction system is 0.05 to 0.5 mol / L, preferably 0.1 mol / L.

[0025] Furthermore, the wavelength used for the reaction is 350-470 nm, preferably 456 nm.

[0026] Furthermore, the reaction temperature is 10-80°C, preferably 45°C.

[0027] The inert gas includes argon, nitrogen and the like.

[0028] The invention has the following advantages: the raw materials are greener and easier to obtain, the product yield is high, and the reaction conditions are mild. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further analyzed and explained below through specific embodiments.

[0030] Example 1: Synthesis of cobalt catalyst precursor

[0031]

[0032] Add CoCl2 (1.3 g, 10 mmol), dimethylglyoxime (2.6 g, 22 mmol) and 50 mL of acetone to a 100 mL round-bottom flask, and blow air into the reaction solution while stirring. Add acetone during the reaction to supplement the volatilization of acetone during the reaction. After 1 h of reaction, put the round-bottom flask into ice water and let it stand for 20 min, then filter it, wash it with ice acetone, and then dry it at room temperature to obtain a green solid Co(dmgH)2Cl2.

[0033] Example 2: Synthesis of cobalt catalyst

[0034]

[0035] Add Co(dmgH)2Cl2 (1.1 g, 3 mmol) and 30 mL of methanol to a 100 mL round-bottom flask, and then add 4-methoxypyridine (720 mg, 6.6 mmol). After stirring the reaction at room temperature for 30 min, add 50 mL of water, and place the round-bottom flask in ice water for 10 min. Then filter and wash with water / acetone (2:1, V / V) and anhydrous ether, and finally dry at room temperature to obtain brown solid Co(dmgH)2(4-OMe-py)Cl.

[0036] Embodiment 3-7:

[0037] The operation process is similar to that of Example 2, except that 4-methoxypyridine is replaced by different pyridines to prepare Co(dmgH)2pyCl, Co(dmgH)2DMAPCl, Co(dmgH)2(4- t Bu-py)Cl, Co(dmgH)2(4-CN-py)Cl and Co(dmgH)2(3,5-Me-py)Cl.

[0038] Embodiment 8:

[0039]

[0040] 39.6 mg (0.3 mmol) of 2-acetoxypropionic acid, 4.5 mg (5 mol%) of PC1 and 6.5 mg (5 mol%) of Co(dmgH)2(4-OMe-py)Cl were added to a 10 ml Shrek tube, and then 3 mL of DME and 166 μL of water were added under an Ar atmosphere. The reaction system was irradiated with blue light for 24 hours at 25°C. After the reaction, the conversion rate of 2-acetoxypropionic acid was 40% and the yield of vinyl acetate was 8% according to liquid chromatography.

[0041] Embodiment 9:

[0042]

[0043] 39.6 mg (0.3 mmol) of 2-acetoxypropionic acid, 3.4 mg (1 mol%) of PC2, 6.5 mg (5 mol%) of Co(dmgH)2(4-OMe-py)Cl, and 97.7 mg (0.3 mmol) of Cs2CO3 were added to a 10 ml Shrek tube, and then 3 mL of DME and 166 μL of water were added under an Ar atmosphere. The reaction system was irradiated with blue light for 24 hours at room temperature. After the reaction was completed, levulinic acid was added as an internal standard, and then analyzed by gas chromatography. The conversion rate of 2-acetoxypropionic acid was 99%, and the yield of vinyl acetate was 69%.

[0044] Embodiment 10-13:

[0045] The operation process is similar to that of Example 9, except that PC2 is replaced by a different photosensitizer. The reaction effects are shown in Table 1.

[0046]

[0047] Embodiment 14-18:

[0048] The operation process is similar to that of Example 9, except that Co(dmgH)2(4-OMe-py)Cl is replaced by different cobalt catalysts. The reaction results are shown in Table 2.

[0049]

[0050] Embodiment 19-29:

[0051] The operation process is similar to that of Example 9, except that Cs2CO3 is replaced by different bases. The reaction results are shown in Table 3.

[0052]

[0053] Embodiment 30-37:

[0054] The operation process is similar to that of Example 9, except that the DME:H2O (18:1) reaction solvent is replaced with a different reaction solvent. The reaction results are shown in Table 4.

[0055]

[0056] Examples 38-40:

[0057] The operation process is similar to that of Example 9, except that the amount of photosensitizer used is different. The reaction effects are shown in Table 5.

[0058]

[0059] Embodiment 41-43:

[0060] The operation process is similar to that of Example 9, except that the amount of cobalt catalyst used is different. The reaction results are shown in Table 6.

[0061]

[0062] Embodiment 44-46:

[0063] The operation process is similar to that of Example 9, except that the amount of alkali used is different. The reaction results are shown in Table 7.

[0064]

[0065] Embodiment 47-49:

[0066] The operation process is similar to that of Example 9, except that the concentration of 2-acetoxypropionic acid in the reaction system is different. The reaction results are shown in Table 8.

[0067]

[0068] Embodiment 50-53:

[0069] The operation process is similar to that of Example 9, except that the reaction light source is different. The reaction effects are shown in Table 9.

[0070]

[0071] Examples 54-57:

[0072] The operation process is similar to that of Example 9, except that the reaction temperature is different. The reaction results are shown in Table 10.

[0073]

Claims

1. A method for preparing vinyl acetate, characterized in that The steps include: 2-acetoxypropionic acid, a photosensitizer, a cobalt catalyst, a base and a solvent are added into a reaction container, and vinyl acetate is prepared by decarboxylation and dehydrogenation reaction under an inert gas atmosphere and blue light irradiation; The photosensitizer structural formula is as follows: ； Wherein, R1-R8 is selected from hydrogen or C1-C6 alkyl, alkoxy or halogenated alkane; X is selected from halogen; Ar represents an aromatic group; Y - represents anion; The general structural formula of the cobalt catalyst is shown below: ； Wherein, L represents a ligand, and X is selected from halogen.

2. The preparation method according to claim 1, characterized in that: The photosensitizer is selected from the following structures: 。 3. The preparation method according to claim 1, characterized in that: The cobalt catalyst is selected from the following structures: 。 4. The preparation method according to claim 1, characterized in that: The base is selected from one or more of Cs2CO3, Na2CO3, NaHCO3, K2CO3, KHCO3, K3PO4, K2HPO4, Na3PO4, Na2HPO4, Me4NOH, Me4NHCO3, and (Me4N)2CO3.

5. The preparation method according to claim 1, characterized in that: The solvent is selected from one or more of halogenated alkanes, ethers, and amides.

6. The preparation method according to claim 5, characterized in that: The solvent is selected from a mixed solvent of one or more of ethylene glycol dimethyl ether, tetrahydrofuran, acetonitrile, diethylene glycol dimethyl ether, dimethyl sulfoxide, N,N-dimethylformamide, N,N-diethylacetamide and ethylene dichloride.

7. The preparation method according to claim 6, characterized in that: The solvent is a mixed solvent consisting of ethylene glycol dimethyl ether and water, and the volume ratio of the two is 18:

1.

8. The preparation method according to claim 1, characterized in that: The molar ratio of 2-acetoxypropionic acid to the photosensitizer is 200:1-5:1, and the molar ratio of 2-acetoxypropionic acid to the cobalt catalyst is 50:1-5:

1.

9. The preparation method according to claim 1, characterized in that: The concentration of 2-acetoxypropionic acid in the reaction system is 0.05~0.5 mol / L.

10. The preparation method according to claim 1, characterized in that: The reaction was carried out under the protection of inert gas; the wavelength used for the reaction was 350-470 nm.

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